The objective of this project is to determine the role of specific antibodies and non-specific cell receptor analogs in breast milk in protecting infants from rotavirus infection. The specific aims are as follows: 1) Determine the serotype distribution of asymptomatic and symptomatic rotavirus infection in breastfed and formula fed infants; 2) Evaluate the association between milk antibodies and rotavirus serotypes in infants who acquire asymptomatic and symptomatic infection with rotavirus; 3) Characterize intestinal secretory IgA (sIgA) antibody response to rotavirus proteins of the infecting serotype during the course of natural rotavirus infection and evaluate cross-reaction with other rotavirus serotypes including those of the major rotavirus vaccine strains. Associations will be examined between intestinal immunity and type of feeding during naturally acquired asymptomatic and symptomatic rotavirus infection; 4) Determine if immunization protects against rotavirus infection: a) Demonstrate in mice the ability of maternal milk antibodies (natural and immunization induced) to different rotavirus antigens to protect suckling infant mice from homologous and heterologous rotavirus infection. b) Identify a population of pregnant women and, following postpartum immunization of these women with rotavirus vaccine, determine the systemic and milk antibody response and the protection of milk and intestinal secretory antibodies against naturally acquired infection in breastfed infants; 5) Characterize non-immune factors in milk which may interfere with rotavirus infection. The importance of this subproject is that it will permit us to define the roles of milk antibodies against specific rotavirus proteins and cell receptor analogs in protection of infants from rotavirus infection.